1. Technical Field of the Invention
The present invention relates to a resolver unit which detects a rotational position, and a resolver using it, and more particularly to a resolver unit which has transformer windings, and in which the axial length is shortened, and a resolver using it.
2. Description of the Related Art
FIG. 6 shows a related art resolver comprising transformer windings for a power supply.
FIG. 6 is a fragmentary sectional view of the related art resolver having a cylindrical stator assembly, and a rotor assembly which is placed coaxially with the cylindrical stator assembly.
In FIG. 6, the resolver 100 comprises the cylindrical stator assembly 101, the rotor assembly 102 which is placed coaxially with the stator assembly 101, and a transformer portion 103.
The transformer portion 103 has an inner core 104, and an outer core 105 which is placed coaxially with the inner core.
A stator portion has a structure in which the outer core 105 and the stator assembly 101 are axially built in a cylindrical housing 106.
A rotor portion has a structure in which the inner core 104 and the rotor assembly 102 are axially built in a shaft 107.
In the transformer portion 103, a winding of the inner core 104 is connected to a rotor winding of the rotor assembly 102 by a crossover wire. Winding portions of the resolver are coaxially placed. In order to prevent the shaft from being eccentric, therefore, two bearings 108 are placed with being axially separated from each other.
In the example shown in FIG. 6, the inner core 104, the rotor assembly 102, and the two bearings 108 are continuously disposed in the axial direction. Consequently, the axial length is prolonged, and the stator assembly 101 and the rotor assembly 102 which are cylindrically placed, and the inner core 104 and the outer core 105 have a complicated structure, thereby causing a problem that the whole resolver cannot be miniaturized.
In order to shorten the axial direction, therefore, a disk type resolver or a flat type resolver has been proposed (for example, JP-A-8-136211 and JP-A-5-010779, hereinafter referred to “JPA'211” and “JPA'779” respectively).
FIG. 7 is a sectional view of a related art flat type resolver which is described in below.
In FIG. 7, the stationary side has a stationary core 111 and a stationary sheet coil 113.
The stationary core 111 comprises a magnetic plate 112 which is made of a material having an excellent high-frequency iron loss characteristic, such as disk-like ferrite.
The stationary sheet coil 113 is fixed to a side face of the magnetic plate 112 by an adhesive agent or the like. In the stationary sheet coil 113, a primary winding 114 of a rotary transformer portion A, and a detection winding 115 of a signal generating portion B are formed from a flat plate-like conductor by a printed wiring produced with etching, printing, or a press work, and bonded to the front and rear faces of a disk-like insulating substrate made of polyimide. An insulating process using a polyimide resin or the like is applied over the surface of the conductor.
The rotary side has a rotary core 116 and a rotary sheet coil 118, and is fixed to a shaft 119. The rotary core 116 is a disk-like core which is opposed to the stationary core 111 via an air gap, and comprises a magnetic plate 117 in the same manner as the stationary core 111.
The rotary core 116 is fixed to the shaft 119 at the center, and supported via a bearing 121 by a bracket 120 fixed to the stationary core 111.
The rotary sheet coil 118 is fixed to a side face of the magnetic plate 117 by an adhesive agent or the like. In the rotary sheet coil 118, a secondary winding 122 of the rotary transformer portion A, and an exciting winding 123 of the signal generating portion B are similarly formed by a printed wiring, and bonded to the front and rear faces of a disk-like insulating substrate 124 made of polyimide. An insulating process using a polyimide resin or the like is applied over the surface of the conductor. In the case where the fixation of the stationary core 111 and the stationary sheet coil 113, and that of the rotary core 116 and the rotary sheet coil 118 are conducted by an adhesive agent, the adhesive agent has a thickness of about 25 μm, and hence the magnetic air gap is increased. This causes the power consumption to be increased.
The related art flat type resolver of FIG. 7 has the following problems.    (1) In the case where the fixation of the stationary core 111 and the stationary sheet coil 113, and that of the rotary core 116 and the rotary sheet coil 118 are conducted by an adhesive agent, the adhesive agent has a thickness of about 25 μm. Therefore, the stationary sheet coil 113 may be attached with being inclined with respect to the face of the stationary core 111 by a thick layer of the adhesive agent, or the rotary sheet coil 118 may be attached with being inclined with respect to the face of the rotary core 116 by a thick layer of the adhesive agent. In such a case, the gap between the rotary and stationary sides cannot be made uniform, and there is a problem in that the magnetic coupling characteristic between the rotary and stationary sides is distorted by a degree corresponding to the inclination.    (2) The surface of each conductor is provided with the insulating process using a polyimide resin or the like. Therefore, the thickness of the resin layer on the conductor causes the gap between the rotary and stationary sides not to be uniformly formed, and the axial length between the rotary and stationary sides is prolonged. Consequently, there is a problem in that the magnetic coupling characteristic between the rotary and stationary sides is impaired.    (3) The primary winding 114 of the rotary transformer portion A, and the detection winding 115 of the signal generating portion B are supported on the magnetic plate 112, and the secondary winding 122 of the rotary transformer portion A, and the exciting winding 123 of the signal generating portion B are supported on the magnetic plate 117. Magnetic members forming the magnetic path are restricted to only the magnetic plates 112 and 117 on the both sides.
Therefore, the distance from the winding on one side to the magnetic plate on the other side is relatively long. When the number of rotations is decreased and the output power of the transformer is reduced, consequently, magnetic fluxes crossing the magnetic plates 112 and 117 are hardly produced. Hence, a magnetic path which forms magnetic fluxes effectively interlinking with the secondary winding 122 and the detection winding 115 is insufficient, and leakage magnetic fluxes are increased.
Since each winding is formed from a flat plate-like conductor by a printed wiring produced with etching, printing, or a press work, the number of turns cannot be increased. Therefore, it is difficult to increase magnetic fluxes generated by the winding.
Consequently, it has been requested to develop a resolver in which the axial length is shortened so as not to impair the magnetic coupling characteristic between the rotary and stationary sides, and a winding generates a large number of magnetic fluxes. JP-A-57-052639 (hereinafter referred to “JPA'639” shows an example which serves as a reference.
FIG. 8 is a view showing the configuration of the example disclosed in JPA'639.
In a resolver 130 of FIG. 8, a rotary transformer 131 and a resolver body 132 are concentrically placed around a rotation shaft 133 with placing the rotary transformer in the inner side and the resolver body in the outer side, thereby reducing the thickness of the resolver 130. A rotor portion 134 of the rotary transformer 131 is fixed to the rotation shaft 133, and a stator portion 135 is fixed to an annular stator portion support member 138 which is inwardly projected from an end plate portion 137 of a case 136. A rotor portion 139 of the resolver body 132 is fixed to a rotor portion support member 140 which is supported integrally by the rotation shaft 133, and a stator portion 143 of the resolver body 132 is fixed to the case 136. The rotor portion support member 140 comprises a disk portion 141 fixed to the rotation shaft 133, and an annular portion 142 which is continuously disposed on the circumference of the disk portion 141.    (1) In the resolver of FIG. 8, in the direction from the center axis to the radially outer side, the rotor portion 134 of the rotary transformer 131 disposed on the rotation shaft 133, the stator portion 135 of the rotary transformer 131 disposed on the stator portion support member 138, the rotor portion 139 of the resolver body 132 disposed on the rotor portion support member 140, and the stator portion 143 of the resolver body 132 disposed on the case 136 are placed in this order. In this configuration, gaps are produced between the rotor portion 134 of the rotary transformer 131 and the stator portion 135, between the stator portion support member 138 and the rotor portion support member 140, and between the rotor portion 139 of the resolver body 132 and the stator portion 143. These gaps are hardly kept to respective appropriate values because the number of the gaps is large.    (2) In order to supply the electric power generated in the rotary transformer 131 to an exciting coil of the resolver body 132, a coil winding of the rotor portion 134 of the rotary transformer 131 is connected to that of the rotor portion 139 of the resolver body 132 by a crossover wire.    The crossover wire is extended along the rotor portion support member 140. Since the length of the crossover wire is large, the crossover wire is susceptible to the wind pressure during rotation, and also to vibrations during rotation. Therefore, damage such as breakage easily occurs in the crossover wire.    (3) In order to couple the rotor portion 139 of the resolver body 132 and the rotor portion 134 of the rotary transformer 131 in a predetermined relationship, the rotor portion 139 of the resolver body 132 is disposed on the rotor portion support member 140, the rotor portion 134 of the rotary transformer 131 is disposed on the rotation shaft 133, and the rotor portion support member 140 and the rotation shaft 133 are coupled together.
As the minimum configuration for forming a resolver, a configuration where the case 136 in which the stator portions 135, 143 are disposed, and the rotor portion support member 140 in which the rotor portions 134, 139 are disposed, and the rotation shaft 133 are coupled together is required. Even when multiplexing is considered on the basis of the minimum configuration, such multiplexing is hardly realized because means for coupling the rotation shaft is problematic.